1) Field of the Invention
The invention relates to a method of mixing flows with each other in a papermaking process, according to which method a first flow is fed through a tube, and one or more second flows is/are fed into the first flow via a feed opening which is in connection with the space limited by said tube.
The invention further relates to a mixer comprising a tube, through which the first flow of the papermaking process is conveyed; and a feed opening which is in connection with the space limited by the tube and with a feed channel for mixing a second flow into the first flow through the feed opening.
The invention further relates to feeding equipment of a head box of a paper machine, comprising a tube through which a first flow is conveyed to the head box; a feed opening which is in connection with the space limited by the tube and with the feed channel for feeding a second flow into the first flow through the feed opening; and a process component, such as a pump or screen, which is arranged in said tube before the head box.
2) Description of Related Art
There are a plurality of objects in different papermaking processes in which other pulp flows or various additives, such as coloring, filling and retention agents, are mixed into the main flow formed of liquid and pulp. It is typical to mix retention chemicals that bind solid matter particles into the fiber suspension flow headed for the head box of a paper machine, which retention chemicals allow improvement of the retention of fines and filler agents in the wire section of the paper machine. The mixing of different components can be performed with what are called tube mixers. Thus, the additive is conveyed into the pulp flow through tubes or nozzles arranged on the side of the pulp tube. However, the arrangement has not brought about a mixing result that would be sufficiently good. Attempts have also been made to feed a jet of additive at a very fast rate into the pulp flow, whereby the desired effect would have been for the additive jet to better penetrate into the pulp flow. Unfortunately, the problem here is that some additives, such as a retention agent, adhere to the surface of the fiber or other solid matter in an undesirable manner when being fed at a fast rate, which results in what is called flat conformation, for example, and the additive no longer has the desired retention relative to the filling agent or fines. Further, the result may be undesired degradation of the retention agent because of too great shear forces. Due to these aspects, the final product is subjected to detrimental variation of the profile.
Further, in order to improve the mixing, injection nozzles can be used that extend some distance into the inside of the pulp tube. The problem is, however, that the ends of the nozzles inside the pulp tube gather impurities, which makes the feed of the additive more difficult and deteriorates the quality of the final product.
An object of this invention is to provide a novel and an improved arrangement for mixing two separate flows in a tube.